Field of the Invention
The present invention relates to an intake air mass estimation apparatus for motorcycle that views a throttle valve provided in an intake passage of an engine for motorcycle as an orifice (aperture) to estimate the air mass passing through the orifice.
Description of the Related Art
Conventionally, as a method for estimating the intake air mass for an motorcycle, a throttle speed method (a method of estimating the intake air mass from the throttle opening and the engine rotation speed) or a speed density method (a method of estimating the intake air mass from the intake pressure and the engine rotation speed) or both have been used. In recent years, with the tightened exhaust gas regulation and requirements of the marketplace for fuel efficiency improvement, there has been a need for accurate measurement of the intake air mass for proper fuel injection. A known method for accurately estimating the air mass taken into an engine is an intake air mass estimation method employing a throttle model. Thus, the inventors studied the introduction of a throttle model intake air mass estimation method used for a car into a motorcycle.
In general, a car includes a multi-cylinder engine. A multi-cylinder four-stroke engine for car (an engine that performs intake, compression, combustion and exhaust during 720 degrees of crank angle rotation) is characterized in that a plurality of times of intakes and combustions are performed during 720 degrees of crank angle rotation, that the flywheel is configured to be heavy in order to suppress the rotation fluctuation of the engine, and that a plurality of cylinders are connected to the downstream of the throttle valve or the throttle valve downstream has a large inner volume due to the presence of a surge tank.
In the multi-cylinder engine characterized as above, the rotation fluctuation of the engine (variation in the engine rotation speed during 720 degrees of crank angle rotation) is smoothed by the combustions of the multiple cylinders overlapping with one another each having a phase difference from the adjacent cylinder during 720 degrees of crank angle rotation and the heavy flywheel. Furthermore, the throttle valve downstream pressure fluctuation (variation in the throttle valve intake pressure during 720 degrees of crank angle rotation) is smoothed by the intakes of the multiple cylinders overlapping with one another each having a phase difference from the adjacent cylinder during 720 degrees of crank angle rotation and the large inner volume of the throttle valve downstream functioning as a filter.
Therefore, the throttle model intake air mass estimation is calculated using the average engine rotation speed and the average throttle valve downstream pressure as indicated by the following equation:Q=m(P1,P2ave)*(60/NEave).
In the above equation, Q is the air mass used for one combustion, P1 is the throttle valve upstream pressure, P2ave is the average throttle valve downstream pressure, m is the mass flow rate of the gas passing through the throttle valve as a function of P1, P2ave, and NEave is the average engine rotation speed.
By the way, for example, JP-A-5-222998 (Patent Document 1) describes a way of viewing a throttle valve as an orifice and estimating the air mass passing through the orifice from the flow passage opening area of the orifice and the pressures of the upstream and downstream of the orifice, based on a fluid mechanics equation. This document also describes a way of estimating the throttle valve downstream pressure depending on the crank angle in order to capture the throttle downstream pressure that varies along with the piston stroke, also taking into consideration the small inner volume of the throttle valve downstream.
JP-A-2006-37911 (Patent Document 2) describes an intake valve model in which the throttle valve downstream pressure is estimated using a throttle model and the intake valve is viewed as an orifice to estimate the air mass passing through the intake valve from the throttle valve downstream pressure, the cylinder internal pressure and the intake valve opening area, in which the case of gas blowing back from the cylinder into the intake passage downstream of the throttle valve is taken into consideration.
[Patent Document 1] JP-A-5-222998
[Patent Document 2] JP-A-2006-37911
Some motorcycles have a single-cylinder engine. In general, a single-cylinder four-stroke engine for motorcycle is characterized in that intake and combustion are performed only once during 720 degrees of crank angle rotation, that the flywheel for suppressing the rotation fluctuation of the engine is lightweight, and that there is no surge tank downstream of the throttle valve and, since there is a short distance from the throttle valve to the cylinder of the engine, the throttle valve downstream has a small inner volume.
In the single-cylinder engine characterized as above, the engine rotation fluctuation occurs because of only one combustion during 720 degrees of crank angle rotation and the lightweight flywheel. Also, the throttle valve downstream pressure fluctuation occurs because of only one intake during 720 degrees of crank angle rotation and the small inner volume of the throttle valve downstream.
Accordingly, there is a problem with a motorcycle having a single-cylinder engine in which the intake air mass cannot be accurately determined through the calculation of the throttle model intake air mass estimation using the average throttle valve downstream pressure and the average engine rotation speed.
However, although the Patent Document 1 takes into consideration the variation in the throttle valve downstream pressure depending on the crank angle, it mentions nothing about the engine rotation fluctuation.
Also, the Patent Document 2 mentions the intake valve model in which the intake valve is viewed as an orifice to determine the air mass flow passing through the opening intake valve by performing integration at predetermined intervals, but it mentions nothing about the throttle model. Thus, it does not describe the estimation of the air mass passing through the throttle valve during 720 degrees of crank angle rotation taking into consideration the throttle valve downstream pressure fluctuation and the engine rotation fluctuation.
Also, the Patent Document 2 mentions the case in which air is blown back from the cylinder into the intake passage downstream of the throttle valve, but it mentions nothing about the case in which air is blown back from the throttle valve downstream to the throttle valve upstream.